package com.taxigang.client.css;

/*
 * Copyright 2008 Google Inc.
 * 
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not
 * use this file except in compliance with the License. You may obtain a copy of
 * the License at
 * 
 * http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations under
 * the License.
 */

import com.allen_sauer.gwt.log.client.Log;
import com.google.gwt.dom.client.Document;
import com.google.gwt.dom.client.HeadElement;
import com.google.gwt.dom.client.LinkElement;
import com.google.gwt.user.client.Command;
import com.google.gwt.user.client.DeferredCommand;
import com.google.gwt.user.client.Timer;
import com.google.gwt.user.client.Window;
import com.google.gwt.user.client.ui.Label;
import com.google.gwt.user.client.ui.RootPanel;

/**
 * A utility class that loads style sheets.
 */
public class StyleSheetLoader {
	/**
	 * A {@link Timer} that creates a small reference widget used to determine
	 * when a new style sheet has finished loading. The widget has a natural width
	 * of 0px, but when the style sheet is loaded, the width changes to 5px. The
	 * style sheet should contain a style definition that is passed into the
	 * constructor that defines a height and width greater than 0px.
	 */
	private static class StyleTesterTimer extends Timer {
		private Command callback;
		private Label refWidget;
		private String css;
		private int counter;

		/**
		 * Create a new {@link StyleTesterTimer}.
		 * 
		 * @param refStyleName the reference style name
		 * @param callback the callback to execute when the style sheet loads
		 */
		public StyleTesterTimer(String css, String refStyleName, Command callback) {
			this.callback = callback;
			this.css = css;

			// Create the reference Widget
			refWidget = new Label();
			refWidget.setStyleName(refStyleName);
			refWidget.getElement().getStyle().setProperty("position", "absolute");
			refWidget.getElement().getStyle().setProperty("visibility", "hidden");
			refWidget.getElement().getStyle().setProperty("display", "inline");
			refWidget.getElement().getStyle().setPropertyPx("padding", 0);
			refWidget.getElement().getStyle().setPropertyPx("margin", 0);
			refWidget.getElement().getStyle().setPropertyPx("border", 0);
			refWidget.getElement().getStyle().setPropertyPx("top", 0);
			refWidget.getElement().getStyle().setPropertyPx("left", 0);
			RootPanel.get().add(refWidget);
		}

		@Override
		public void run() {
			// Redisplay the reference widget so it redraws itself
			//refWidget.setVisible(false);
			refWidget.setVisible(true);

			// Check the dimensions of the reference widget
			Log.info("StyleTesterTimer:run"+refWidget.getOffsetHeight());
			if (refWidget.getOffsetWidth() > 0) {
				RootPanel.get().remove(refWidget);

				// Fire the callback in a DeferredCommand to ensure the browser has
				// enough time to parse the styles. Otherwise, we'll get weird styling
				// issues.
				DeferredCommand.addCommand(callback);
			} else {
				if (counter++ > 20){
					Window.alert("could not load css: "+css);
				}
				schedule(10);
			}
		}
	}

	/**
	 * Convenience method for getting the document's head element.
	 * 
	 * @return the document's head element
	 */
	public static native HeadElement getHeadElement()
	/*-{
    return $doc.getElementsByTagName("head")[0];
  }-*/;

	/**
	 * Load a style sheet onto the page.
	 * 
	 * @param href the url of the style sheet
	 */
	public static void loadStyleSheet(String href) {
		Log.info("loadStyleSheet");

		LinkElement linkElem = Document.get().createLinkElement();
		linkElem.setRel("stylesheet");
		linkElem.setType("text/css");
		linkElem.setHref(href);
		getHeadElement().appendChild(linkElem);

	}

	/**
	 * Load a style sheet onto the page and fire a callback when it has loaded.
	 * The style sheet should contain a style definition called refStyleName that
	 * defines a height and width greater than 0px.
	 * 
	 * @param href the url of the style sheet
	 * @param refStyleName the style name of the reference element
	 * @param callback the callback executed when the style sheet has loaded
	 */
	public static void loadStyleSheet(String href, String refStyleName,
			Command callback) {
		if (href == null){
			callback.execute();
		} else {
			Log.info("loadStyleSheet"+href);	  
			loadStyleSheet(href);
			waitForStyleSheet(href, refStyleName, callback);

		}
	}

	/**
	 * Detect when a style sheet has loaded by placing an element on the page that
	 * is affected by a rule in the style sheet, as described in
	 * {@link #loadStyleSheet(String, String, Command)}. When the style sheet has
	 * loaded, the callback will be executed.
	 * 
	 * @param refStyleName the style name of the reference element
	 * @param callback the callback executed when the style sheet has loaded
	 */
	public static void waitForStyleSheet(String css,String refStyleName, Command callback) {
		Log.info("waitForStyleSheet");	  
		new StyleTesterTimer(css, refStyleName, callback).run();
	}
}
